Neuromuscular Junction Diseases (MG, LEMS, Botulism) Flashcards Preview

Neurology > Neuromuscular Junction Diseases (MG, LEMS, Botulism) > Flashcards

Flashcards in Neuromuscular Junction Diseases (MG, LEMS, Botulism) Deck (21)
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1
Q

Prominent feature of diseases affecting NMJ?

A

Fatigueability.

2
Q

What is myasthenia graves?

A

Progressive autoimmune disorder due to anti-AChR antibodies resulting in early saturation at the NMJ and inadequate muscle activation with increasing nerve stimulation

3
Q

What condition is myasthenia gravis associated with?

A

Thymoma

  • 15% have thymic neoplasia
  • 85% have thymic hyerplasia
4
Q

Epidemiology of myasthenia gravis?

A

Bimodal onset:

  • 20s (mostly women)
  • 60s (mostly men)
5
Q

What are the signs and symptoms of myasthenia graves?

A
  • Fatigueable, symmetric or asymmetric weakness w/o reflex changes, sensory changes or coordination abnormalities
  • Ocular (diplopia/ptosis), bulbar (dysarthria/dysphagia), proximal limb weakness
6
Q

What may exacerbate MG symptoms?

A

Infection, pregnancy, menses, various drugs

7
Q

Ix in MG work up?

A
  • Tensilon test (assess for improvement over 2min following edrophonium injection)
  • EMG: repetitive stimulation, decremental response
  • RFTs (FVC to monitor adequacy of resp effort over time)
  • Anti-AChR Ab
  • MUSK Ab if Anti-AChR -ve
  • CT/MRI (thymic changes)
8
Q

Treatment of MG?

A
  • Thymectomy (85% show improvement or remission)
  • Symptomatic relief: acetylcholinesterase inhibitor (e.g. pyridostigmine)
  • Immunosuppression (steroids, or steroid sparing therapy)
  • IVIg and plasmapharesis for crises
9
Q

Prognosis MG?

A
  • 30% spontaneous remission

- W/ Rx: life expectancy equal to normal, QoL may vary

10
Q

What is Lambert Eaton Myasthenic Syndrome?

A

Autoimmune disorder due to antibodies against presynaptic voltage-gated calcium channels causing decreased ACh release at NMJ

11
Q

What is Lambert Eaton Myesthenic syndrome associated with?

A

Small cell carcinoma of the lung

12
Q

Signs and symptoms of LEMS?

A
  • Weakness of sk muscle w/o sensory or coordination abnormalities
  • Reflexes diminished or absent BUT increase after muscle contraction
  • Bulbar/occular muscles affected in 25% (v 90% in MG)
  • Prominent anticholinergic Sx
13
Q

Anticholinergic Sx? (e.g. in LEMS)

A
  • Dry mouth
  • Impotence
  • Constipation
  • Blurred vision
14
Q

Ix in ?LEMS?

A
  • Edrophonium: no response
  • EMG
  • Screen for malignancy (esp SmC lung Ca)
15
Q

EMG findings in LEMS?

A
  • Rapid (>10Hz) repetitive stimulation: incremental response

- Post exercise facilitation: incremental response with exercise

16
Q

Rx LEMS?

A
  • Tumour removal
  • ACh modulation (increased release = diaminopyridine, decreased destruction = pyridostigmine)
  • Immunomodulation (steroids, plasmapharesis, IVIg)
17
Q

What causes botulism?

A

Toxin produced by spores of Clostridium botulinum bacteria found in soil and water; enter body through wounds or improperly prepared food.

18
Q

Signs and symptoms of botulism?

A
  • Diff w/ convergence, ptosis, paralysis of extraocular muscles
  • Dilated, poorly reactive pupils
  • Other autonomic dysfunction: jaw weakness, dysarthria, dysphagia
  • Spread to trunk/limbs: ado pain / N/ V; symmetric weakness w/ paralysis and decreased deep tendon reflexes
  • Anticholinergic Sx
19
Q

Ix botulism?

A
  • Blood test for toxin

- Stool culture

20
Q

Rx botulism?

A
  • Botulinum anti-toxin

- Supportive therapy as required

21
Q

What is MuSK myasthenia?

A

Abx binding to MuSK cause the subunits of ACh receptor to deaggregate and lose function